The present invention relates to a method of and an apparatus for electric discharge machining in which a voltage is applied between a tool electrode and a workpiece so as to generate an electric discharge and execute machining (xe2x80x9cworkingxe2x80x9d). More particularly, this invention relates to a method of and an apparatus for electric discharge machining which can achieve a high speed response in X-axis, Y-axis and Z-axis directions for driving an electrode, and improve machining accuracy.
In electric discharge machining, a tool electrode and a workpiece are arranged in a machining fluid, a voltage is applied therebetween and an electric discharge is generated so as to erode the workpiece. In an electric discharge machining apparatus, in order to machine a desired shape while maintaining a stable machining state, a driving apparatus which adjusts positions of the tool electrode or the workpiece is provided. FIG. 17 is a schematic view which shows an outline structure of a conventional electric discharge machining apparatus which is described, for example, in pages 63-64 of xe2x80x9cDischarge Machining Techniquexe2x80x94From Basics to Future Developmentxe2x80x9d issued by Nikkan Kogyo Shinbun, Ltd (1997).
In FIG. 17, reference numeral 101 denotes a tool electrode, reference numeral 102 denotes a workpiece, reference numeral 103 denotes a machining fluid, reference numeral 104 denotes a machining tank, reference numeral 1201 denotes an electrode mounting section which mounts the tool electrode 101, reference numeral 501 denotes a head section which supports the electrode mounting section 1201, reference numeral 502 denotes a head drive section which drives the tool electrode 101, the electrode mounting section 1201 and the head section 501, reference numeral 503 denotes a column section, reference numeral 504 denotes a column driving section which drives the tool electrode 101, the electrode mounting section 1201, the head section 501, the head driving section 502 and the column section 503, reference numeral 505 denotes a saddle section, reference numeral 506 denotes a saddle driving section which drives the tool electrode 101, the electrode mounting section 1201, the head section 501, the head driving section 502, the column section 503, the column driving section 504 and the saddle section 505, and reference numeral 507 denotes a bed section. The head driving section 502, the column driving section 504 and the saddle driving section 506 are, for example, constituted by an AC motor and a ball screw, and respectively constitute a driving section which positions the electrode in Z direction, a driving section which positions in Y direction and a driving section which positions in X direction. Further, reference numeral 119 denotes a machining power supply which supplies a machining energy to the tool electrode 101 and the workpiece 102, reference numeral 120 denotes a machining state detecting apparatus which detects a machining state, reference numeral 1202 denotes a servo amplifier which supplies a drive current to each of the electrode mounting section 1201, the head driving section 502, the column driving section 504 and the saddle driving section 506 so as to execute positioning, and reference numeral 1203 denotes a control apparatus giving a command value to the servo amplifier 1202 and the machining power supply 119. Further, reference numeral 122 denotes an electric discharge machining process progressed between the tool electrode 101 and the workpiece 102.
FIG. 18 shows a gap control system which controls machining state in the electric discharge machining apparatus shown in FIG. 17. In FIG. 18, reference numeral 301 denotes an electric discharge machining process section, reference numeral 302 denotes a machining state detecting section, reference numeral 303 denotes a reference value setting section, reference numeral 304 denotes a machining pass setting section, reference numeral 1301 denotes a machining control section, reference numeral 1302 denotes a XYZ driving control section, reference numeral 1303 denotes a current amplifier section, reference numeral 1304 denotes a XYZ driving section, and reference numeral 1305 denotes a XYZ driving apparatus constituted by the XYZ driving control section 1302, the current amplifier section 1303 and the XYZ driving section 1304. The electric discharge machining process section 301 corresponds to the electric discharge machining process 122, the machining state detecting section 302 corresponds to the machining state detecting apparatus 120, the XYZ driving control section 1302 and the current amplifier section 1303 correspond to the servo amplifier 1202, and the XYZ driving section 1304 corresponds to the head driving section 502, the column driving section 504 and the saddle driving section 506, respectively. Further, the reference value setting section 303, the machining pass setting section 304 and the machining control section 1301 are constructed in the control apparatus 1203. Further, y indicates a state variable of the electric discharge machining process, ym indicates a detected value detected by the machining state detecting section 302, r indicates a reference value set by the reference value setting section 303, e indicates a deviation determined from the reference value r and the detected value ym, Rp indicates a machining pass vector set by the machining pass setting section 304, Up indicates a position command value to the XYZ driving control section 1302, Uc indicates a current command value to the current amplifier section 1303, Ic indicates a current amount supplied to the XYZ driving section 1304, St indicates a position detected value obtained from the XYZ driving section 1304, and Mp indicates an electrode position operating amount operated by the XYZ driving section 1304. The position command value Up to the XYZ driving control section 1302 is determined by the machining control section 1301 on the basis of the deviation e and the machining pass vector Rp. Since the machining pass vector Rp is given by a Cartesian coordinate system (XYZ), the position command value Up is in the same Cartesian coordinate system (XYZ). Further, the position detected value St is the detected value in the X direction, the Y direction and the Z direction. Accordingly, in the XYZ driving control section 1302, the position command value Up and the position detected value St are compared, and the current command value Uc to the current amplifier section 1303 is determined. The current command value Uc is given to each of three current amplifiers for the head driving section 502, the column driving section 504 and the saddle driving section 506. That is, in the conventional gap control system shown in FIG. 18, it is made such as to detect, for example, an average gap voltage by the machining state detecting section 302, and move the tool electrode by the XYZ driving apparatus 1305 so that the detected value coincides with a predetermined reference value, thereby achieving a stable machining state.
However, the machining state irregularly changes, and in order to maintain a stable machining state, a high speed response of the XYZ driving apparatus becomes important. When a stable machining state can not be maintained, a short-circuit state, a continuous arc state or the like is frequently generated, and an effective electric discharging state contributing to the machining is reduced, so that the machining speed is reduced. Further, since the short-circuit state, the continuous arc state or the like is frequently generated, a crack or a pit is formed on the machined surface, or an abnormal wear of a tool electrode is locally generated, so that a reduction of machining surface quality or a deterioration of machining accuracy is caused. When a high speed response of the XYZ driving apparatus can not be expected, since it is intended to maintain a stable machining state by selecting the machining condition in which a gap distance during machining becomes comparatively large, it is hard to achieve the machining at high accuracy.
The Patent Publication of Japanese Patent No. 2714851 xe2x80x9cDischarge Machining Control Devicexe2x80x9d discloses a technology for solving the problems in the high speed response of the tool electrode driving apparatus explained above. It is disclosed in this publication, in order to control a gap between a tool electrode and a workpiece, to constitute a driving system by assembling a plurality of driving mechanisms having different frequency characteristics and moving at least one of the tool electrodes and the workpiece in a coaxial direction. However, this publication does not describe a particular driving mechanism which can achieve a high speed response in all directions of the X direction, the Y direction and the Z direction, and there is not referred to a machining control method or a control apparatus when accompanying with a jump motion or a planetary motion which is used for maintaining the stable machining state.
Further, in the grinding method disclosed in Japanese Patent Application Laid-Open No. H1-234162 (Japanese Application), there is presented a method of executing a cutting motion of a tool to a workpiece at a high speed by providing a magnetic bearing spindle and moving the spindle in a spindle diametrical direction on the basis of a predetermined reference value, in place of a cutting motion of a conventional tool constituted by a motor and a ball screw to the workpiece, in a grinding machine, whereby a machining efficiency and a machining accuracy can be improved. In the electric discharge machining, it is necessary that the tool electrode is driven in the XYZ directions on the basis of the machining pass, and a driving amount is determined on the basis of the electric discharge machining state so that the machining becomes stable. Further, there is such when the driving amount becomes some xcexcm to some tens cm in case of some machinings, and there is such when the machining can not be executed when there is employed the drive amount which can be driven by the magnetic bearing spindle. That is, in accordance with the machining method shown in Japanese Patent Application Laid-Open No. H1-234162 mentioned above, since the structure is not made such as to control the driving direction, it is hard to obtain a good machining result even when being applied to the electric discharge machining.
In the conventional electric discharge machining apparatus, when driving the tool electrode 101 to each of the X-axis, the Y-axis and the Z-axis directions, it is necessary that the head driving section 502 drives the electrode mounting section 1201 and the head section 502 in addition to the tool electrode 101 in the Z-axis direction, the column driving section 504 drives the electrode mounting section 1201, the head section 501, the head driving section 502 and the column section 503 in addition to the tool electrode 101 in the Y-axis direction, and the saddle driving section 506 drives the tool electrode 101, the electrode mounting section 1201, the head section 501, the head driving section 502, the column section 503, the column driving section 504 and the saddle section 505 in the X-axis direction. Accordingly, in order to achieve the response in each of the driving sections, there is a problem that it is necessary to take into consideration an increase of mass of the sections moving in each of the X-axis, the Y-axis and the Z-axis directions together with the tool electrode 101 in addition to the tool electrode 101. The response here becomes a relation response of the head driving section 502 greater than response of the column driving section 504 greater than response of the saddle driving section 506, and the control performance of the machining state is determined on the basis of the response of the saddle driving section 506, so that there is generated an obstacle in view of improving the machining speed and the machining accuracy.
The present invention has been achieved in order to solve the problems as mentioned above. It is an object of this invention is to provide a method of and apparatus for electric discharge machining which can restrict an increase of mass of sections which are required to move in each of X-axis, Y-axis and Z-axis directions together with a tool electrode, which can achieve a high speed response in the X-axis, the Y-axis and the Z-axis directions, and which can improve machining speed and machining accuracy.
According to a first aspect of the present invention, there is provided an electric discharge machining apparatus comprising an electrode mounting unit which mounts a tool electrode, an electrode driving unit which has a radial driving unit which drives the electrode mounting unit in a non-contact manner in a radial direction and a thrust driving unit which drives the electrode mounting unit in a non-contact manner in a thrust direction, a machining state detecting unit which detects an electric discharge machining state, a reference value setting unit which sets a control reference of the electric discharge machining state, a machining pass setting unit which sets a machining pass, and a machining control unit which adjusts a position of the tool electrode by the electrode driving unit while taking into consideration the machining pass set by the machining pass setting unit, so that the detected value detected by the machining state detecting unit coincides with the reference value set by the reference value setting unit. Accordingly, it is possible to restrict a mass increase in the sections which should be driven together with the tool electrode, and to achieve the high speed response in the X-axis, the Y-axis and the Z-axis directions of the electrode driving, it is possible to maintain a stable machining state even when the machining state irregularly changes, and it is possible to obtain an effect of improving the machining speed and the machining accuracy.
A second aspect of the present invention provides an electric discharge machining apparatus comprising an electrode mounting unit which mounts a tool electrode, an electrode driving unit which has a radial driving unit which drives the electrode mounting unit in a non-contact manner in a radial direction and a thrust driving unit which drives the electrode mounting unit in a non-contact manner in a thrust direction, a position adjusting unit which adjusts a position of the electrode driving unit or a workpiece, a machining state detecting unit which detects an electric discharge machining state, a reference value setting unit which sets a control reference of the electric discharge machining state, a machining pass setting unit which sets a machining pass, and a coordination control unit which adjusts a relative position between the tool electrode and the workpiece by coordinating the electrode driving unit with the position adjusting unit while taking into consideration the machining pass set by the machining pass setting unit, so that the detected value detected by the machining state detecting unit coincides with the reference value set by the reference value setting unit. Accordingly, it is possible to achieve the high speed response in the X-axis, the Y-axis and the Z-axis directions of the electrode driving, it is possible to achieve a stable machining state even when the machining state irregularly changes, and it is possible to obtain an effect of improving the machining speed and improving the machining accuracy without being affected by the limitation of the driving stroke of the electrode driving section by adjusting the position of the electrode driving apparatus by the position adjusting apparatus following to the progress of the machining.
A third aspect of the present invention provides the electric discharge machining apparatus according to the second aspect, wherein the coordination control unit has a jump motion control unit which executes a jump motion by the position adjusting unit. Accordingly, it is possible to achieve the high speed response in the X-axis, the Y-axis and the Z-axis directions of the electrode driving. Moreover, it is possible to machine while forcibly discharging any debris staying in the machining gap because of the jump motion so that it is possible to obtain an effect of improving the machining speed and improving the machining accuracy even when the machining depth is increased. Moreover, the machining is not limited by the driving stroke of the electrode driving unit.
A fourth aspect of the present invention provides the electric discharge machining apparatus according to the second aspect, wherein the coordination control unit has a planetary motion control unit which executes a planetary motion by the electrode driving unit. Accordingly, it is possible to maintain a more stable machining with planetary motion on the basis of the high speed response in the X-axis, the Y-axis and the Z-axis directions, and it is possible to obtain an effect of improving the machining speed and the machining accuracy.
A fifth aspect of the present invention provides the electric discharge machining apparatus according to the second aspect, wherein the coordination control unit has a jump motion control unit which executes a jump motion by the position adjusting unit and a planetary motion control unit which executes a planetary motion by the electrode driving unit. Accordingly, it is possible to achieve the high speed response in the X-axis, the Y-axis and the Z-axis directions of the electrode driving. Moreover, it is possible to machine while forcibly discharging any debris staying in the machining gap because of the jump motion so that it is possible to obtain an effect of improving the machining speed and improving the machining accuracy even when the machining depth is increased. Moreover, the machining is not limited by the driving stroke of the electrode driving unit.
A sixth aspect of the present invention provides the electric discharge machining apparatus according to the first aspect and the second aspect, wherein the electrode driving unit has a rotation driving unit which rotates the electrode mounting unit and a rotation detecting unit which detects at least one of an angle of rotation and an angular velocity of rotation, and the machining control unit or the coordination control unit has a rotation control unit. Accordingly, it is possible to achieve the high speed response in the X-axis, the Y-axis and the Z-axis directions of the electrode driving. Moreover, it is possible to machine while forcibly discharging, any debris staying in the machining gap because of the jump motion so that it is possible to obtain an effect of improving the machining speed and improving the machining accuracy even when the machining depth is increased. Moreover, the machining is not limited by the driving stroke of the electrode driving unit.
A seventh aspect of the present invention provides an electric discharge machining method made so as to drive an electrode mounting unit which mounts a tool electrode in a non-contact manner in a radial direction and drive the electrode mounting unit in a non-contact manner in a thrust direction, adjust a position of a driving unit or a workpiece, and adjust a position of the tool electrode with respect to the workpiece while taking into consideration a set machining pass, so that a detected value of an electric discharge machining state coincides with a set reference value of the electric discharge machining state. Accordingly, it is possible to restrict a mass increase in the sections which should be driven together with the tool electrode, and to achieve the high speed response in the X-axis, the Y-axis and the Z-axis directions of the electrode driving, it is possible to maintain a stable machining state even when the machining state irregularly changes, and it is possible to obtain an effect of improving the machining speed and improving the machining accuracy.
An eighth aspect of the present invention provides an electric discharge machining method made so as to, drive an electrode mounting unit which mounts a tool electrode in a non-contact manner in a radial direction and drive the electrode mounting unit in a non-contact manner in a thrust direction, adjust a position of a driving unit or a workpiece, and adjust a position of the tool electrode with respect to the workpiece while taking into consideration a set machining pass, so that a detected value of an electric discharge machining state coincides with a set reference value of the electric discharge machining state by coordinating the driving unit with the adjusting unit. Accordingly, it is possible to achieve the high speed response in the X-axis, the Y-axis and the Z-axis directions of the electrode driving, it is possible to achieve a stable machining state even when the machining state irregularly changes, and to adjust the position of the electrode driving apparatus based on the progress of the machining by the position adjusting apparatus, whereby it is possible to obtain an effect of improving the machining speed and improving the machining accuracy without being affected by the limitation of the driving stroke of the electrode driving section.
A ninth aspect of the present invention provides an electric discharge machining apparatus comprising, an electrode mounting unit which has a through hole which inserts a wire-like electrode therethrough and which has a holding and feeding mechanism of the electrode, an electrode driving unit which has a thrust driving unit which drives the electrode mounting unit at least in a non-contact manner in a thrust direction, a machining state detecting unit which detects an electric discharge machining state, a reference value setting unit which sets a control reference of the electric discharge machining state, a machining control unit which adjusts a position of the tool electrode by the electrode driving unit so that the detected value detected by the machining state detecting unit coincides with the reference value set by the reference value setting unit, and an electrode supply control unit which adjusts holding or feeding of the electrode. Accordingly, it is possible to achieve the high speed response in thrust direction, and it is possible to always maintain a stable machining state even when the machining state irregularly changes.
A tenth aspect of the present invention provides the electric discharge machining apparatus according to the ninth aspect, comprising a tool electrode automatic supplying unit which automatically supplies the wire-like electrode to the through hole provided in the electrode driving unit. Accordingly, in addition to the effects of the ninth aspect, it is possible to continuously and effectively execute a hole machining.
An eleventh aspect of the present invention provides the electric discharge machining apparatus according to the ninth aspect or the tenth aspect, wherein the electrode driving unit is provided with a rotation driving unit which rotates the electrode mounting unit. Accordingly, in addition to the effects of the ninth aspect or the tenth aspect, it is possible to perform stable machining by rotating the electrode when machining the hole.